default requires 2 arguments, 1 provided

The solution for this is noted below

default requires 2 arguments, 1 provided

Solution

You have an extra space which causes the error.

value="{{ form.username.value|default_if_none: '' }}"

should be
value="{{ form.username.value|default_if_none:'' }}"

Try other methods by searching on the site. That is if this doesn’t work